The invention relates to a brake disc for a disc brake, in particular for rail vehicles. This contains a hub body with a radially outwardly extending hub flange with axially parallel openings in which screws may be arranged in order to connect a brake ring flange of a brake ring to the hub body, said brake ring flange being arranged radially overlapping and axially adjacent the hub body. It further relates to a brake ring for a disc brake, in particular for rail vehicles containing a radially extending brake ring flange with axially parallel openings in which screws may be arranged in order to connect a hub flange of a hub body to the brake ring, said hub flange being arranged radially overlapping and axially adjacent the brake ring flange.
Disc brakes of the above mentioned type are for example known from DE 26 20 623 A1 (FIGS. 1 and 2). They consist of a hub body which is arranged in a rotationally fixed manner on the shaft of the axle of a vehicle, as well as a brake ring connected to the hub body. The brake ring on at least one outer side comprises a friction surface on which brake shoes engage and by way of a suitable pressure on the friction surface may exert the desired braking effect. The connection between the hub body and the brake ring is effected via a screwing of the hub flange with the brake ring flange. The mentioned flanges are radially distant from the hub body or brake ring, overlap in the radial direction and are arranged axially adjacent one another. The details xe2x80x9cradialxe2x80x9d and xe2x80x9caxialxe2x80x9d or xe2x80x9caxially parallelxe2x80x9d relate to the rotational axis of the brake disc (the same as the axis of the shaft on which the brake disc is attached), which as a rule is also an axis of symmetry of the brake disc. Furthermore the flanges may be designed peripherally in a continuous manner as well as peripherally in a wave-like manner, wherein in the latter case they consist of adjacent lugs. The screws for fastening the brake ring on the hub body pass through openings in the hub flange and in the brake ring flange, these openings being essentially aligned to one another.
It is known that with disc brakes of the mentioned type, with braking procedures the brake ring expands on account of the occuring heating, whereas the hub body does not experience any comparable expansion. A multitude of designs are known for accommodating or for compensating the thermal expansions occuring between the hub flange and the brake ring flange.
Thus for example DE-B 10 31 337 shows a disc brake of the above mentioned type with which the screwing between the hub flange and the brake ring flange is designed such that a radial relative movement between both bodies is possible. In particular there are provided radial slots in the brake ring flange distanced equally over the circumference in which the screws which pass through it may travel radially. However with such a design there exists the danger that with thermal expansions the screws may lose their parallel position to the axis of the disc brake. Thus for example the screw heads may retain their position relative to the hub flange on which they rest, whilst the screw section lies in the brake ring flange and is displaced radially outwards by this on thermal expansion. This leads to considerable bending stresses of the screws which may lead to an increased wear, premature fatigue and in the worst case to a failure of the screws.
For reducing the mentioned bending stresses of the screws, in DE-A 28 28 137 it is known in a disc brake of the initially mentioned type to mount the screw heads as well as nuts in spherical bearing shells, by which means the screws may be pivoted out of their axially parallel bearings essentially without bending and shear stresses. This embodiment form however is very complicated and thus expensive and with thermal expansions leads to undesired changes in the pretension of the screws.
From DE 34 32 501 C2 there is further known a disc brake of the initially mentioned type with which the brake ring flange is arranged movable with thermal expansion between the hub flange and a separate tension ring, wherein the screws axially tension the hub flange against the tension ring. The respective ends of the screws are thus mounted in the hub flange or in the tension ring and thus in two elements which as a rule are not subjected to a relative movement on thermal expansion. It is however disadvantageous that additional means for torque transmission mentioned type to mount the screw heads as well as nuts in spherical bearing shells, by which means the screws may be pivoted out of their axially parallel bearings essentially without bending and shear stresses. This embodiment form however is very complicated and thus expensive and with thermal expansions leads to undesired changes in the pretension of the screws.
From DE 34 32 501 C2 there is further known a disc brake of the initially mentioned type with which the brake ring flange is arranged movable with thermal expansion between the hub flange and a separate tension ring, wherein the screws axially tension the hub flange against the tension ring. The respective ends of the screws are thus mounted in the hub flange or in the tension ring and thus in two elements which as a rule are not subjected to a relative movement on thermal expansion. It is however disadvantageous that additional means for torque transmission must be provided between the hub body and the tension ring so that no bending stresses of the screws occur perpendicular to the radial direction. On account of these means the constructional effort is increased and the assembly is made more difficult. With disc brakes ventilated at the inside, the tension ring may considerably handicap the supply of cooling air to the brake disc. Furthermore there also exists the possibility that with thermal expansion, the forces on the tension ring occur assymetrically with respect to the rotational axis of the disc brake and that on account of this the undesired bending stresses indeed do arise.
From DE-OS 20 60 352 there is known a multi-part brake disc with which on a hub there are provided radially outwardly extending lugs which have axially parallel openings in order to fasten an overlappingly arranged lug of a brake ring by way of corresponding screws, wherein in each case two lugs distanced from one another are in each case provided with an opening through which the ends of the screw may be held. At the same time one envisages designing the fastening screws for the brake ring consisting of brake ring elements as fitting bolts. In order to design the screw connection such that it is axially free of play, may be readjusted in limits and additionally is tensionally locked, at the same time each lug is tensioned against the end face of the hub via bushings.
Against this background it was the object of the present invention to improve a hub body, a brake ring and a brake disc of the initially mentioned type with simple design means in a manner such that with thermal expansions of the brake the axial parallelity of the screws which connect to brake ring flange to the hub flange is ensured. arranged a retaining element with all, but at least with three openings arranged distributed over the circumference.
With the brake disc according to the invention thus both ends of the screws which connect the hub flange to the brake ring flange are fixed relative to the hub body. The first end of the screw which may for example be the screw head, is mounted in an opening on the hub flange. The screw then passes through the brake ring flange, and its second end is held in the retaining element which is fixed on the hub body and transmits this fixation onto the end of the screw. By way of the radial fixing of the screws at both ends their axially parallel position is ensured even with thermal expansions of the brake ring. This is also the case with the use of several retaining elements if the forces should not occur symmetrically with respect to the rotational axis of the brake disc. By way of radial guides according to claim 4 it is ensured that the brake ring always remains centred relative to the axis of the brake disc even with thermal expansions.
According to a first embodiment form of the retaining elements according to the invention these may be designed as a radially outwardly extending retaining lug or as a circumferential retaining flange on the hub body. The formation of the retaining element as a retaining lug on the hub body has the advantage that between two such lugs there remains a free space through which cooling air may flow during operation. Furthermore on assembly of the brake disc, in a simple manner a likewise lug-shaped designed brake ring flange may be introduced through the free space into the intermediate space between the hub flange and the retaining elements. The integral formation of the retaining element with the hub body simplifies the assembly of the brake disc since the retaining elements do not need to be assembled separately.
In a further formation of the last mentioned embodiment form the retaining element formed on the hub body may comprise an axially parallel opening with a sleeve arranged therein, wherein the opening in the retaining element is arranged aligned to the corresponding opening in the hub flange. A screw passing through the hub flange and the braking ring flange may be led through the sleeve, wherein the sleeve is then supported on one side on the braking ring flange. The sleeve serves for pretensioning the brake ring against the hub flange. This is effected via the support of the sleeve on the brake ring flange, wherein on the opposite end of the sleeve the screw engages on the screw thread via the screw head or the nut. By way of the mounting in the sleeve the screw at the same time is additionally protected from bending stresses. By way of the fact that the sleeve is arranged in the opening of the retaining element, furthermore an indirect radial fixing of the screw end relative to the hub body is achieved. At the same time the sleeve however remains axially parallel displaceable in the opening of the retaining element, so that it may transmit the desired axial pretension force onto the brake ring flange.
According to a further formation of the above mentioned embodiment form, on the hub flange and/or on the retaining elements there are provided at least three radial guides equally distributed over the cicumference, which may cooperate with corresponding radial guides on the brake ring flange, in order in the case of a thermal expansion to radially guide and, centre the brake ring flange. The equal distribution of the radial guides over the circumference means that for example three such radial guides at a distance of in each case 120xc2x0 are arranged around the rotational axis of the disc brake. The radial guides ensure that although the brake ring may move in the radial direction relative to the hub body and thus may follow a thermal expansion, however no relative rotation of the brake ring about the rotational axis of the brake disc is possible and that the torque transmission between the brake ring and hub body and their relative position in the circumferential direction remains ensured. Simultaneously the radial guides pointing in various radial directions ensure that the brake ring and hub body assume a centered position to one another also with a thermal expansion.
The above mentioned radial guides in each case are preferably formed as two surfaces extending parallel to a radius on the hub flange and/or on a retaining element, which cooperate with corresponding surfaces on the brake ring flange. The extension of the surfaces parallel to a radius proceeding from the rotational axis of the disc brake ensures that the surface exerts a guide in the direction of this radius.
According to a second design form of the retaining element of the present invention, this is formed as an L-shaped retaining bracket which in a first limb comprises an opening for leading through the end of the screw. Furthermore on the hub body there is provided an axially orientated groove in which the second limb of the mentioned retaining bracket may be arranged. The orientation of the groove is defined as the direction from the base of the groove towards its opening, that is to say parallel to the walls of the groove. Of course this embodiment form of the retaining elements may also be combined with the above explained form since the individual retaining elements distributed along the circumference of the hub body are basically independent of one another. The L-shaped retaining bracket is mounted in the axially orientated groove on the hub body in a manner such that it remains movable in the axial direction and is fixed in the radial direction as well as preferably also in the circumferential direction. As a whole then the desired radial fastening of the retaining bracket is achieved, wherein the retaining brackets however simultaneously with the tightening of the screws move axially and thus may transmit the set pretension force onto the brake ring flange. The use of retaining brackets has the advantage that on assembly of the disc brake these may firstly be removed so that the brake ring and disc body may be put together in an unhindered manner. Only on tightening the screws are the retaining brackets then attached after one another. Furthermore by way of the application of the variously dimensioned retaining brackets there may be effected a simple adaptation of the dimensions of the brake ring and hub body.
The invention furthermore relates to a brake ring for a disc brake, in particular for rail vehicles, containing a radially extending brake ring flange with axially parallel openings in which there may be arranged screws in order to connect a hub flange arranged radially overlapping and neighbouring the brake ring flange to the brake ring. The brake ring is characterised in that with at least one opening there is arranged a retaining element which is fixed on the brake ring and by way of which the end of the screw may be held after its passage through the hub flange.
With such a brake ring the two ends of the screws are fixed relative to the brake ring. The brake ring on construction of the disc brake therefore functionally behaves in the same manner as the above explained hub body. The possibilities of design of the hub body explained above may thus be accordingly applied to the brake ring.
Furthermore a brake disc, in particular a brake disc for rail vehicles, containing a hub body as well as a brake ring fastened to this, also belongs to the invention. The brake disc is characterised in that the hub body is designed in the manner explained above and/or in that the brake ring is designed in the manner explained above, and that the end of the screw is held by the retaining element fixed on the hub body or on the brake ring. With such a brake disc by way of the fixation of the screw ends on both sides it is ensured that the screws retain their axially parallel position even with a thermal expansion of the brake ring and, the screws as well as the brake ring remain centered with respect to the axis of the disc brake. Furthermore as explained above with reference to the hub body, one achieves a simplification of the assembly as well as a guarantee of the ventilation of the brake ring.
According to a further embodiment form it is envisaged for the screw to be designed such that firstly the head has a surface which by way of its bearing an a collar of the hub formed specially as a support, there is effected a rotational securement when screwing the nut on and off, and secondly below the head there is incorporated a knurling which on assembly of the screw into the hub digs into the receiver bore and by way of this firmly retains the screw with a press fit in the hub so that on assembly of the brake ring it does not need to be held in position by hand.